1. Field of the Invention
The present invention relates to an inkjet recording apparatus, and more particularly, to technology for supplying satisfactory deaerated ink to an inkjet head.
2. Description of the Related Art
An inkjet recording apparatus that forms an image by ejecting ink from a recording head (an inkjet head) to a recording medium has many merits as follows. An image of high accuracy can be formed by a small recording head in which a plurality of nozzles are arranged at high density. Moreover, by aligning a plurality of recording heads and supplying different inks of a plurality of colors to the recording heads, a color image is obtained by means of a small and inexpensive composition. Furthermore, by aligning heads substantially in a line configuration, it is possible to record over large format recording medium having a broad width.
In an inkjet recording apparatus of this kind, it is important that the ejection of ink from the recording head be stable. In particular, normally, a certain quantity of gas is dissolved into the ink (dissolved gas) and forms gas bubbles inside the ink flow channels and the recording head, which can give rise to negative effects such as inhibiting the flow of ink and producing ejection failures in which no ink is ejected. Therefore, a composition incorporating a deaeration device which performs deaeration processing of the ink supplied to the recording head is adopted, or alternatively the ink to be used is previously subjected to deaeration and then packaged.
Japanese Patent Application Publication No. 11-042795 describes a composition in which a deaeration device is provided at an intermediate point of the ink supply channel for supplying ink inside a tank to an inkjet head, and furthermore, an ink circulation path for returning the ink that has passed through the deaeration device to the tank is provided in order to prevent gas bubbles and dissolved gas in the ink, which give rise to ink ejection failures and ejection instability, from entering into the inkjet head.
Japanese Patent Application Publication No. 2005-059476 describes a composition in which a return flow channel is provided for returning ink to a sub tank from before the ink ejection port in a head section, and furthermore a deaeration device is provided in the return flow channel or a first flow channel (a flow channel that conveys ink from a main tank to the sub tank).
However, in the composition described in Japanese Patent Application Publication No. 11-042795, since deaeration is performed after returning ink to a main tank in which ink is stored or to a sub tank in which ink is held temporarily, then consequently the circulated ink volume becomes large. Therefore, it is necessary to provide a deaeration device having a large capacity and hence there is a drawback in that the apparatus costs become high. Furthermore, there is a possibility that air will dissolve into the ink held in the main tank, and hence there is also a problem of decline in the deaeration efficiency. Moreover, since the deaeration device is provided between the inkjet head and the sub tank, then there are also problems in that a pressure loss occurs in the deaeration device, pressure adjustment in the inkjet head becomes difficult to achieve and the ink ejection state becomes instable. Furthermore, if left for a long period of time, air dissolves again into the ink held in the sub tank, the beneficial effects of deaeration are not obtained and there is a possibility that ejection defects will occur.
Moreover, in the composition described in Japanese Patent Application Publication No. 2005-059476, the deaeration device is not provided in the second flow channel (the flow channel that conveys ink from the ink tank to the head), and therefore although it is possible to prevent pressure loss from the sub tank to the head section, the ink flow channels formed inside the head section is narrower than the other flow channels (the flow channels that connect the main tank and the sub tank, or the flow channels that connect the sub tank and the head section, for instance) and therefore produce greater flow channel resistance, thus restricting the flow volume which can be circulated in each module (head chip). Consequently, if the volume of ink into which gas dissolves in the sub tank per unit time exceeds the volume of ink that is deaerated, then the amount of dissolved gas will not be reduced sufficiently, and ink containing a large amount of dissolved gas will be supplied to the head section, thereby giving rise to ejection defects.
Furthermore, using ink which has already undergone deaeration processing is expensive in itself, and the replenishment and management of the ink involves a great amount of work.